Air pollution has become a major environmental concern due to the huge amount of pollutants produced from vast human activities. It contains numerous combinations of pollutants such as particle matter (PM) of various sizes, chemical mixtures, biological hazards, and etc. Moreover, creation of unexpected chemical compounds due to the photochemical reactions in the polluted air, makes it more and more puzzling to clean the air. These complicated mixtures have posed excessive threats to public health. PM contains small solid particles and liquid droplets with different sizes. Regarding the size, particulate pollutants can be categorized by PM2.5 and PM10-2.5, indicating particle sizes below 2.5 and between 2.5 and 10 respectively. PM2.5 is mainly one of the major pollutants in many developing countries. These particles are commonly composed of organic (e.g. carbon derivatives species such as carbon oxides) and inorganic (e.g. nitrates, sulfates, silicates, etc.) compounds which can seriously influence the air quality, public health, climate change, air visibility and so on. In addition, polluted air includes numerous types of toxic gaseous molecules, such as sulfur oxides (SOx), nitrogen oxides (NOx), carbon oxides (CO and CO2), formaldehyde (HCHO), methane (CH4), and a mixture of other volatile organic compounds (VOCs). These chemicals can undergo various photochemical reactions which may lead to the creation of unexpected hazardous pollutants. Biological hazards including bacteria, viruses, mites, pollen and etc. can trigger many allergic reactions and infectious illnesses such as influenza, measles and chicken pox. Because of the intensive effects of these pollutants on the environment and human health, providing an effective protection, particularly toward improving the indoor air quality, is urgently needed.
Filtration membranes are commonly used to remove the pollutants from the air and improve the quality of the air. Some attempts have been made for enhancing the outdoor personal protection, and improving the indoor air quality. An ideal air filter should have a high removal efficiency of pollutants yet maintaining low resistance to the air flow. Conventional air filters are usually made of micron-size fibers of synthetic plastics such as polyethylene and polypropylene. These air filters are ineffective for removing the toxic gaseous chemicals from the air due to the lack of active functional groups in the structure of the raw materials. These materials are only effective for capturing particulate pollutants based on the four primary physical and size-based filtration mechanisms, including sieving, interception, impaction, and diffusion.
In view of increasing global pollution, a need exist to provide filtration materials that filter both particles and chemical pollutant species, while not significantly reducing air flow.